A variety of control systems for equipment, processing lines, assembly lines and the like have been proposed and utilized to varying degrees. For example, systems based on the use of digital computers and/or microprocessors/microcontrollers are known to provide a reasonably high degree of programmable input/output control for such applications. While the advances in this general field have been relatively great, due to reasons such as safety and conventional design practices, there are a number of undesirable attributes of such conventional control systems.
FIG. 1 illustrates an exemplary control system such as might be found in a piece of processing equipment, such as for fabricating semiconductors. Controller 10 serves to provide control to the equipment by way of interface 16 (which may be a series of wires, etc.) coupled to control terminals of relays distributed through the equipment, and may also receive inputs from sensors in the equipment. Signals to and from the relays and sensors are coupled to controller 10, thereby providing a highly centralized control system for the equipment. In certain of such systems, the connections to the relays and/or sensors are made by way of what are frequently referred to as VME cards 14, which may be added to controller 10 in the desired number and type in order to satisfy the input/output control requirements for the equipment. Controller 10 may be coupled to another computer via interface 12. The inputs and outputs from controller 10 may, in general, be either inputs or outputs, digital or analog, etc.
Such conventional systems, while providing a highly centralized form of control, suffer from various disadvantages. For example, the numerous wires that must pass from cards 14 to the various relays often result in large, bulky and complex wiring harnesses. Bulky and/or complex wiring harnesses, for example, increase manufacturing costs, make changes in the system more difficult, and can result in undesirable compromises in the overall system physical design in order to accommodate the wiring harnesses. In addition, it is often more difficult to implement redundancy with such a centralized control system, and the problems associated with maintenance and/or upgrades to the equipment tend to be complex and difficult.